17.4 - Dihybrid Inheritance Flashcards
What is dihybrid inheritance?
- Dihybrid inheritance refers to the inheritance of two characters, each determined by different genes located on separate chromosomes.
- These characters are passed from one generation to the next, and each gene can assort independently during gamete formation.
What did Gregor Mendel investigate in his dihybrid inheritance experiment?
- Mendel investigated the inheritance of two traits in pea plants:
1) seed shape, where round is dominant to wrinkled
2) seed color, where yellow is dominant to green. - He studied how these two traits were passed on simultaneously.
What were the parent plants used in Mendel’s dihybrid cross experiment?
- Mendel crossed two pure-breeding pea plants:
- one always producing round-shaped, yellow-colored seeds (both dominant traits),
- one always producing wrinkled-shaped, green-colored seeds (both recessive traits).
What were the results of Mendel’s F₁ generation in his dihybrid cross?
- In the F₁ generation, all the offspring had round-shaped, yellow-colored seeds.
- This indicated that the dominant traits (round shape and yellow color) were expressed in all plants.
How many types of gametes were produced in Mendel’s F₂ generation, and why?
- The F₂ generation produced four types of gametes: RG, Rg, rG, and rg.
- This occurred because the genes for seed color and seed shape are located on separate chromosomes, allowing them to assort independently during meiosis.
Why can the alleles for seed shape and seed color combine in various ways during meiosis?
- During meiosis, chromosomes arrange themselves randomly on the equator, allowing any allele of the gene for seed color (G or g) to combine with any allele for seed shape (R or r).
- This randomness leads to different combinations of gametes.
What is the expected phenotypic ratio in Mendel’s dihybrid cross experiment?
- The expected phenotypic ratio for the F₂ generation in Mendel’s dihybrid cross experiment is 9:3:3:1.
- This ratio reflects the combination of the dominant and recessive traits for seed shape and seed color.
How did Mendel’s observed results in his dihybrid cross compare to the theoretical ratio?
- Mendel’s observed results (315:108:101:32) were very close to the theoretical 9:3:3:1 ratio, allowing for statistical error.
- This supported his hypothesis about the independent assortment of alleles.
What is Mendel’s law of independent assortment?
- Mendel’s law of independent assortment states that each member of a pair of alleles can combine randomly with either member of another pair.
- This law explains how genes for different traits assort independently during gamete formation.
What role does fertilization play in dihybrid inheritance?
- Fertilization is a random process in dihybrid inheritance, where any of the four types of gametes from one parent can combine with any of the four types from the other parent, contributing to the genetic diversity seen in offspring.
In fruit flies, a pure breeding variety with red eyes and vestigial (tiny) wings was crossed with a pure breeding variety with pink eyes and normal wings. All the F, flies had red eyes and normal wings. When these F, flies were bred with one another, the F, generation produced the following types and numbers:
- red eyes with vestigial wings 125
- red eyes with normal wings 376
- pink eyes with vestigial wings 41
- pink eyes with normal wings 11
Which characteristics are dominant and which are recessive? Explain your answer?
- Red eyes and normal wings are dominant because these characteristics are expressed in the F1 generation
- while pink eyes and vestigial wings are not expressed in the F2 generation and so these are recessive.
- Also red eyes and normal wings appear around 3 times more often in the F, generation than pink eyes and vestigial wings.
In fruit flies, a pure breeding variety with red eyes and vestigial (tiny) wings was crossed with a pure breeding variety with pink eyes and normal wings. All the F, flies had red eyes and normal wings. When these F, flies were bred with one another, the F, generation produced the following types and numbers:
- red eyes with vestigial wings 125
- red eyes with normal wings 376
- pink eyes with vestigial wings 41
- pink eyes with normal wings 11
Suggest suitable symbols to represent the alleles of the genes involved.
- R for red eyes
- r for pink eyes
- N for normal wings
- n for vestigial wings.
In fruit flies, a pure breeding variety with red eyes and vestigial (tiny) wings was crossed with a pure breeding variety with pink eyes and normal wings. All the F, flies had red eyes and normal wings. When these F, flies were bred with one another, the F, generation produced the following types and numbers:
- red eyes with vestigial wings 125
- red eyes with normal wings 376
- pink eyes with vestigial wings 41
- pink eyes with normal wings 11
Draw two suitable genetic diagrams to explain the results of this experiment.
Why did Gregor Mendel choose pea plants for his genetic experiments?
- Mendel chose pea plants because they were easy to grow and had many contrasting features that could be easily observed.
- Additionally, he could control pollination accurately and use pure-breeding plants for his experiments.
How did Mendel control pollination in his experiments?
- Mendel carefully controlled pollination by transferring pollen from one plant to another using a paintbrush.
- This allowed him to ensure fertilization occurred exactly as he intended in his controlled experiments.
